Genesis EXT port

[Dr.Wily]

Someone know the pinout of the EXT port on Genesis first generation ?

[NFG]

I have this info somewhere...  Most of the pins are the same as the cart port.  Use a multimeter to find about 80% of the connections.  The rest are mostly power and audio, about 5-10 connect to one other chip in the system.

[atom]

What are you planning on doin? Im curious.

[Dr.Wily]

Yes OK, but no !  

I talking about Genesis model 1 (wihtout BIOS)  EXT port for modem device (Sega Channel). No EXP (Mega-CD) port.

This port is the same than joypad port but this is a female plug and pinout is not the same.

This is this EXT port :

http://dr.wily.9online.fr/md_ext.jpg

Do you see what I mean ?

[NFG]

It's just a serial port.  Only one unsupported device ever used it.  I doubt you'll find a pinout or be able to use it for anything.

[Dr.Wily]

For upload purpose, it's an ideal way.

Combined with a RAM cartidge it's easy to upload a ROM or homebrew on it from this EXT port.

Like Famicom Disk Loader for example.

[Aidan]

Trace the wiring from the port then. If it's expecting RS232 voltages, then there'll be a level converter. If it's using standard TTL voltages, then there'll be a UART somewhere.

The second problem will be communicating with the UART in software. If there is no documentation for the interface, you are going to have to guess where it lives in the memory map, as well as how to program the thing up to be able to receive/send anything.

It might be worth seeing if you can find out just how fast the port can go, as a slow serial port is a waste of time. A 4Mbyte image will take about 18minutes to transfer at 38400bps assuming an efficient transfer mechanism. If it's slower than that, then it's probably not worth worrying about.

An alternative is to build a RAM cart that includes a UART in it's memory map. That way the serial hardware is on the cart rather than in the console, and you will know how it works.

[dum dum]

the EXT port is functionaly equal to the 2 joypad ports, that is, the machine realy has 3 joypad compatible ports. as far as i can figure out from http://cgfm2.emuviews.com/txt/gen-hw.txt
pins other than the joypad multiplex pin can be used as outputs

[dum dum]

have a bit of a look at this http://www.retrodev.com/transfer.html
link the joypad port to pc parallel for transfer, so theres a working example of joypad port tinkering

[Kurisu]

That is a 9-Pin din serial port on the back of the Genesis, It was going to be used for a modem that Sega never released here in the states, In Japan it was called the Mega Modem and ran at 2400 baud. Just get a 9 Pin din cable from whatever electronic/computer store and have fun.

[KeepGood]

Just a tiny wee update to the last post :-)

You want to get a D-Type plug, not a DIN.

Please post if anyone finds something to do with the extra port, I'm well into toasting my MD trying something stupid :-)

[NFG]

I had someone request a mod once, where we cut the traces to the serial port and used it as a second video output port.  Worked really well.